Flood inundation modeling of the pasig-potrero river draining from mount pinatubo to the pampanga river basin in the philippines using HEC-RAS

The setting of the Philippines makes it an entryway for atmospheric disturbances originating from the east. These violent disturbances are often accompanied by other hazards that amplify the devastation that already entail such occurrences. Flooding is among the attendant phenomena steered by these meteorological events, and recurring floods are plights that necessitate proactive disaster risk planning and management. Through the conduct of one-dimensional steady-state flow analysis using Hydrologic Engineering Center's River Analysis System (HEC-RAS), inundation related to three storm events, with varying rainfall conditions, was characterized in terms of depth and extent. This was done to compensate for the limitations of presently available event-based flood risk data for the Pasig-Potrero river, which drains from Mount Pinatubo to the Pampanga River Basin in Central Luzon. Critical depths were reached when flooding rose to around 7.99, 8.68 and 9.58 m in the modeling of tropical depression Milenyo, typhoon Frank and typhoon Santi, respectively. The total area encompassed by the floodwaters manifesting from the aforesaid meteorological scenarios was consequently determined to be 9.36, 9.83 and 15.58 sq. km, respectively. It was in Barangay Cabetican within the Municipality of Bacolor, however, that flooding was particularly extensive. An increasing trend was observed in the area exposed to flooding when the model was manipulated in the order of escalating peak discharge value. For the said barangay, 50% of the area was initially found inundated under tropical depression Milenyo. This progressed to 53% under typhoon Frank, and to 72% under typhoon Santi. Inundation may have been governed by different interplaying factors, but within the context of HEC-RAS, flooding may have been primarily attributed to river morphology as supported by the notable channel bars downstream, which act to obstruct the free flow of water. Moreover, the simulations do not necessarily replicate the exact same inundation patterns that occurred during the actual storm events; however, by incorporating the same rainfall conditions that characterized the meteorological scenarios, flood simulation was carried out given the present conditions of the river. © 2020 Taiwan Joint Irrigation Associations.